Pigments, Resins and Carriers Part II
In developing a paint system the appropriate pigments are suspended in a material called a Binder or Resin. Resin binds the pigment particles and forms the smooth and adherent surface that we expect. There are many types of chemistry suitable to prepare paint but only a few can withstand the rigors of roof exposure and the destructive UV rays of the sun. Three types are in widespread use today: Polyester, Polyester Silicone, and Fluropolymer. Let’s take a further look at each of these:
- Polyester An organic binder, polyesters are moderate price with moderate performance. As an exterior coating, these finishes are typically used on low-demand products such as residential rainware, soffits, fascia, or sometimes siding. Polyesters are often formulated in light colors such as white or beige. The Metal Construction Association (MCA) would rate the best examples of polyester paints as “Standard” meaning they pass 5-year Florida Exposure Fence testing.
- Polyester Silicone The addition of a significant amount (30%) of silicone to a polyester finish increases cost, decreases hardness/flexibility and most importantly increases color holding and chalk resistance. An important chemistry, polyester silicone provides long term durability especially for sidewalls. Use on roofing, especially for high visibility applications such as residential or consumer commercial is a little questionable for these finishes, especially in Southern locations. They also meet the MCA criteria for Standard Performance.
- Fluropolymer (aka Kynar 500® and Hylar 5000® PVDF resin-based finishes) When it comes to metal roofing, this is the best known and best performing finish category. These finishes offer top performance in terms of flexibility and maintaining color. They are ready for the most challenging needs. They are definitely the answer for the types of “difficult” colors that are usually used residentially such as dark earthtones, low gloss finishes, metallics and even “saturated” colors such as intense reds or blues. These are the only coatings that satisfy the MCA criteria for Premium System including 10 years Florida 45 Degree South actual data.
- Carrier – This is the part of a paint system that you never see! The carrier gives proper fluidity, assists with adhesion to the substrate, and adjusts the speed of evaporation / drying. When the metals used for roofing are painted, the carrier disappears during the heat curing, or “baking,” process.
In many cases, distributors and contractors handling metal roofing are completely unaware of the various paint systems. As a result, they may anecdotally make performance claims which are unrealistic and misleading. Homeowners considering a metal roof should always know and understand the chemistry, attributes, and expected performance of the finish on the product they choose. Manufacturers and contractors who care about the metal roofing industry will gladly explain and guide homeowners through this process.
Kynar 500® is a registered trademark belonging to Arkema Inc.
Hylar 5000® is a registered trademark belonging to Solvay